The present invention relates to connectors for oil well casing and more specifically to a box end connector.
Presently in the oil and gas drilling industry large diameter casing is utilized to support borehole walls of the well. Casing sections making up a casing string are joined either by standard API couplings or welded on pin and box connectors with a specialized thread.
The standard API coupling is a short (10" or less) piece of pipe threaded at both ends on the inside diameter. This coupling is used to join two sections of casing which are threaded both ends with threads mating to the coupling.
The connector type devices are mating pins and boxes which are welded to opposite ends of each section of casing. Current connectors on the market are differentiated by specialized thread forms, each of which is not compatible with API threads nor are they interchangeable with each other.
The standard API couplings have several drawbacks most notably of which is the threaded make-up on both sides of the coupling. With two made-up threads between each section of casing the potential for thread leakage, or improper make-up, is doubled. Additionally standard couplings have square shoulders and these shoulders hang up on the restricted borehole of the blowout preventer when running the casing in a well. The same problems exists if the casing must be pulled out of the well, for it must pass through the same blowout preventer. The hanging up of the couplings causes delay in running the pipe and is potentially dangerous to the pipe and running equipment.
Where specialized connectors are used the outside diameter of most connectors is larger than the standard borehole of the blowout preventer and either the preventer must be removed while running the casing or an oversized preventer installed with a lower pressure rating. In either case the practice is less safe than using the standard blowout preventer.